A generally pipe expanding device is used for expanding a front of a pipe to a desired shape so that a separate assembling member is connected thereto, when connecting pipes whose sizes are identical or different from each other.
In order to expand a thin, light and small-sized pipe made of metal material such as feeding/discharging pipes or smoke pipes, a conventional pipe expanding device is divided into two parts, and an expanding portion is formed at each part by means of bending or bulging using the pressing process, and then it is united by means of welding or soldering. In other case, one side of a pipe is cut in a length direction and spread out, and then an expanding portion is formed at the other side and then united by means of argon welding or soldering. However, such methods do not give uniform quality since the exposed expanding portion is not irregular, and deteriorates appearance since the argon-welding or soldering region is exposed as it is. In addition, workability is deteriorated and the number of processes is increased due to complicated and cumbersome individual procedures such as shaping of the expanding portion, separation of the pipe, and uniting, thereby lowering productivity and causes increase of costs.
In addition, a conventional expanding method employs pressing a pipe with a separately fabricated mold. In this case, since a circumference is expanded to form a protruded pipe expanding portion, work is troublesome and not economical due to increase of costs. Moreover, the expanding work should be conducted suitably for work conditions and its use. However, since the same expanding method as for expanding the entire pipe or for a large-caliber pipe for industrial heavy equipment is applied to a partially expanding condition or a large pipe expanding work for industrial use, which is inefficient.